Method and system for preparing high-activity magnesium oxide by double-temperature-zone gradient calcination of magnesite

Abstract

The application discloses a method and system for preparing high-activity magnesium oxide by double-temperature-zone gradient calcination of magnesite, and belongs to the technical field of magnesium oxide preparation. The method comprises the following steps: raw material pretreatment, first-temperature-zone pulse type pre-decomposition, transition zone temperature rise, second-temperature-zone complete decomposition and cooling collection. The method realizes the staged accurate decomposition of magnesite by the double-temperature-zone gradient calcination process, an alternating magnetic field with an axial gradient distribution is applied in the first-temperature-zone to promote the pre-decomposition of magnesite and optimize the crystal structure of magnesium oxide. Constant-temperature complete decomposition is carried out in the second-temperature-zone, the carbon dioxide concentration is monitored in real time, and the residence time is dynamically adjusted. The system comprises a raw material pretreatment unit, a cyclone type double-temperature-zone calcination reactor, a pulse heating and magnetic field auxiliary system, a temperature control and atmosphere adjusting system and a rapid cooling and product collection unit. The method disclosed by the application can prepare magnesium oxide products with high activity, large specific surface area and fine particle size, significantly improves the product performance and improves the controllability and stability of the production process.

Description

Technical Field

[0001] This invention relates to the field of magnesium oxide preparation technology, specifically to a method and system for preparing highly active magnesium oxide by dual-temperature gradient calcination of magnesite. Background Technology

[0002] Magnesium oxide is an important inorganic chemical product with wide applications in refractory materials, building materials, rubber products, pharmaceuticals, chemicals, and environmental protection. With continuous advancements in industrial technology and increasingly stringent product quality requirements, the market demand for highly active magnesium oxide is growing, leading to more stringent requirements for its performance indicators. Magnesite is a naturally abundant magnesium mineral resource, primarily composed of magnesium carbonate, which can be calcined at high temperatures to produce magnesium oxide. The thermal decomposition of magnesite is a complex physicochemical process involving multiple steps, including crystal structure destruction, chemical bond breaking, gas generation and release, and the formation and growth of new phases. During calcination, magnesium carbonate decomposes to release carbon dioxide gas and simultaneously generates magnesium oxide crystals. The manner and conditions of the decomposition reaction directly affect the microstructure and macroscopic properties of the final product. An ideal calcination process should achieve complete decomposition of magnesite while controlling the growth of magnesium oxide crystals to form a product structure with high activity, large specific surface area, and fine particle size.

[0003] Traditional magnesite calcination processes primarily employ rotary kilns and vertical kilns, conducting isothermal calcination under a single temperature condition. While these traditional processes offer simple equipment and relatively easy operation, they suffer from numerous limitations in terms of product quality and production efficiency. Single-zone isothermal calcination cannot provide differentiated temperature conditions for different stages of the magnesite decomposition process, resulting in a lack of precise control over the process. In the initial stages of calcination, excessively high temperatures can cause rapid decomposition of the magnesite particles, forming a dense magnesium oxide layer. This dense structure hinders further decomposition of the internal magnesium carbonate, leading to incomplete decomposition or requiring extended calcination times. In the later stages of calcination, improper temperature control can easily lead to excessive growth and sintering of magnesium oxide grains, reducing the specific surface area and activity of the product, failing to meet the demands of high-end applications. Existing isothermal heating methods are significantly insufficient in promoting uniform magnesite decomposition. While a constant temperature field sustains the reaction, it lacks the ability to regulate the internal stress state of the particles, making it difficult to effectively promote the formation of internal cracks and gas diffusion channels. When magnesite particles decompose under isothermal conditions, a significant difference in decomposition rates between the surface and interior often occurs. Surface decomposition products easily form a barrier layer, hindering the escape of carbon dioxide gas from the particle interior, resulting in residual undecomposed magnesium carbonate inside and affecting product purity. Simultaneously, magnesium oxide crystals formed under isothermal heating lack the driving force for directional growth, resulting in a relatively dense crystal structure with low porosity, which is unfavorable for forming a porous structure with a high specific surface area. Traditional calcination processes generally lack effective means to control the growth process of magnesium oxide crystals. The microstructural characteristics of magnesium oxide, including grain size, crystal orientation, and pore distribution, have a decisive influence on its macroscopic properties. Under conventional heat treatment conditions, newly formed magnesium oxide crystals mainly grow spontaneously driven by thermodynamic factors, making it difficult to achieve precise control over crystal morphology and structure. Grain growth follows the principle of minimizing energy, with large grains engulfing smaller grains, resulting in a large grain size, small specific surface area, and a limited number of active sites in the final product. The lack of external field assistance to influence ion migration and crystal orientation limits the optimization of the product's microstructure, preventing the full realization of the material's performance potential. Magnesite's thermal decomposition reaction has a high activation energy, and the reaction rate is relatively slow at certain temperatures, requiring a long calcination time to achieve complete decomposition. Extending the calcination time not only reduces production efficiency and increases energy consumption, but also easily leads to grain coarsening due to prolonged high-temperature treatment, which is detrimental to obtaining highly reactive products.

[0004] Traditional calcination processes rely solely on temperature and time for extensive control, lacking real-time monitoring and feedback adjustment of key intermediate parameters. The degree of magnesite decomposition can be characterized by carbon dioxide release, but existing processes often lack online monitoring of gas composition, making it impossible to understand the reaction progress in a timely manner and forcing the use of experience to set fixed calcination times. Open-loop control cannot adapt to fluctuations in raw material properties and changes in production conditions, easily leading to under-decomposition or over-processing, resulting in poor product quality stability. Establishing an intelligent feedback control system based on real-time monitoring of process parameters to achieve precise control of the calcination process is crucial for improving product quality consistency. While traditional rotary kilns are widely used, the residence time of materials within the kiln is relatively wide. Some materials have insufficient residence time, leading to incomplete decomposition, while others have excessive residence time, resulting in over-sintering, affecting the overall uniformity of product quality. In vertical kilns, materials descend slowly in a piled-up state, resulting in uneven internal temperature and atmosphere distribution, potentially creating temperature dead zones or poor gas flow in localized areas. The reactor lacks a structural design that promotes material agitation and gas-solid contact, which limits the improvement of heat and mass transfer efficiency and affects the uniformity of the decomposition reaction and the overall quality of the product.

[0005] Therefore, it is urgent to develop new technical solutions to overcome the limitations of existing magnesite calcination technology for preparing magnesium oxide, and to achieve comprehensive optimization of key performance indicators such as product activity, specific surface area, and particle size distribution, as well as precise control of the production process. Summary of the Invention

[0006] To address the problems existing in the background art, the present invention provides a method for preparing highly active magnesium oxide by dual-temperature gradient calcination of magnesite, comprising the following steps:

[0007] S1: Raw material pretreatment; crush the magnesite raw material to a particle size of 3-8mm and preheat it to 200-300℃ in a preheating device; S2: First temperature zone pulse pre-decomposition; send the preheated magnesite into the first temperature zone and pulse-heat it within a temperature range of 650-750℃, with a temperature fluctuation range of ±20-40℃, while applying an alternating magnetic field, with a residence time of 15-25min, real-time monitoring of CO2 concentration, and adjustment of temperature and residence time based on CO2 concentration feedback; S3: Transition zone heating; the material... Heating to 850-880℃ at a heating rate of 5-15℃ / min; S4: Complete decomposition in the second temperature zone; The material is fed into the second temperature zone and treated at a constant temperature of 850-950℃ for 25-40 min. The CO2 concentration at the outlet is monitored and the residence time is dynamically adjusted according to the CO2 concentration to reduce the CO2 concentration at the outlet to below 3%; S5: Cooling and collection; The calcined magnesium oxide is rapidly cooled to below 200℃ at a cooling rate of 20-50℃ / min, and highly active magnesium oxide is obtained after sieving.

[0008] Furthermore, in step S1, a cobalt salt solution is sprayed onto the surface of the magnesite before preheating. Specifically, this involves spraying a cobalt nitrate or cobalt acetate solution onto the surface of the crushed magnesite through an atomizing nozzle. The amount of cobalt salt added... Calculate using the following formula: ;in, The mass (g) of cobalt in the cobalt salt; The mass of the magnesite raw material is (g); α is the cobalt doping coefficient, ranging from 1 to 10; the material is stirred or turned over simultaneously during spraying to ensure uniform distribution of the cobalt salt solution; after spraying, the material is immediately sent to a preheating device, where the cobalt salt solution evaporates during the preheating process at 200-300℃, and cobalt ions adhere to the surface of the magnesite particles, forming a cobalt doping precursor, so that the cobalt salt is uniformly dispersed and adheres to the particle surface during the preheating process of the sprayed magnesite.

[0009] Furthermore, in step S2, the specific operations of the first temperature zone pulse pre-decomposition, CO2 concentration feedback adjustment, and magnetic field gradient control are as follows: Pulse temperature control: setting the reference temperature of the first temperature zone. The target temperature is set within the range of 650-750℃, and the actual temperature is achieved by periodically adjusting the heating power. exist Fluctuations within a range, of which The temperature range is 20-40℃, with a temperature fluctuation period. Determine using the following formula: in, The temperature fluctuation period is in seconds. The pulse frequency (Hz) is used for CO2 concentration feedback control. In the first temperature zone, 3-5 CO2 concentration monitoring points are set along the material flow direction to collect the CO2 concentration values ​​at each monitoring point in real time and calculate the weighted average concentration. ,according to With target concentration Deviation adjustment dwell time, adjusted dwell time Calculate using the following formula: ;in, The adjusted dwell time (min); The baseline dwell time (min); This is an adjustment coefficient, with a value ranging from 0.15 to 0.25. The weighted average CO2 concentration (%); The target CO2 concentration is set at 5-7%; when At this time, the residence time can be extended by reducing the material conveying rate or increasing the baffle opening; when At the same time, the residence time is shortened by increasing the material conveying rate or reducing the baffle opening; magnetic field gradient control: the first temperature zone is divided into three sections along its length: inlet section, middle section, and outlet section, with a length ratio of 1:1.5:1; a magnetic field strength is applied to the inlet section. The magnetic field frequency is 0.02-0.03T. The frequency is 10-20 Hz; a magnetic field strength is applied in the middle section. The magnetic field frequency is 0.04-0.06T. The frequency is 25-35 Hz; the magnetic field strength applied at the exit section is... The magnetic field frequency is 0.06-0.08T. The frequency is 40-50Hz; each magnetic field is controlled by an independent frequency converter, and the magnetic field strength and frequency between adjacent sections are smoothly transitioned, with a transition zone length of 0.3-0.5m; the alternating magnetic field is started at the same time as the material enters the first temperature zone, so that the material undergoes pre-decomposition under the combined action of pulse temperature and gradient magnetic field. Under the action of gradually increasing magnetic field, it goes through three stages: pre-decomposition, crystal orientation and lattice rearrangement, which promotes CO2 escape and oriented growth of MgO crystals.

[0010] Furthermore, in step S3, the specific operation of heating the transition zone is as follows: controlling the material outlet temperature from the first temperature zone. Linear heating to the inlet temperature of the second temperature zone heating rate Calculate using the following formula: ;in, The heating rate is expressed in °C / min. The inlet temperature for the second temperature zone is 850-880℃. The outlet temperature of the first temperature zone is 730-760℃. The transition time (min) is 5-10 min. During the heating process, the atmosphere is kept flowing, and the flow rate increases with the temperature to promote the discharge of residual CO2 and prevent the product from being recarbonized.

[0011] Furthermore, in step S4, the specific operation for the complete decomposition of the second temperature zone is to constantly control the temperature of the second temperature zone within a set value within the range of 850-950℃. The heating power is adjusted in real time through a PID control algorithm. The control algorithm is as follows: ;in, The adjusted heating power (kW); The reference heating power is (kW). This is the proportionality coefficient; The integral coefficient; These are the differential coefficients; Temperature deviation (°C) ; The actual measured temperature (°C); This is the integral of the temperature deviation over time. The derivative of the temperature deviation with respect to time; CO2 concentration is monitored at the outlet of the second temperature zone. ,according to Dynamically adjust material residence time The formula is adjusted as follows: ;in, This is the adjusted dwell time (in minutes); The baseline dwell time (min); The adjustment factor is set to a value between 0.2 and 0.3. Export CO2 concentration (%); For reference concentration, the value is 3%.

[0012] Furthermore, in step S5, the specific operation of cooling and collecting is as follows: the outlet temperature of the second temperature zone is... The magnesium oxide is fed into a cooling device and cooled to the outlet temperature by indirect water cooling or forced air cooling. Cooling rate Controlled by the following formula: ;in, Cooling rate (°C / min); The inlet temperature of the cooler is (°C). The outlet temperature of the cooler should be controlled between 180-220℃. The cooling time (min) is used to maintain the cooling rate within the range of 20-50℃ / min by adjusting the flow rate of the cooling medium. Protective gas is introduced during the cooling process to prevent magnesium oxide from absorbing moisture. After cooling, magnesium oxide is classified by a vibrating screen to separate different grades of products with particle sizes of <1mm, 1-3mm, and 3-5mm.

[0013] This invention also designs a system for preparing highly active magnesium oxide by dual-temperature zone gradient calcination of magnesite, comprising: a raw material pretreatment unit, including a crusher, a screening machine, a cobalt salt spraying device, and a cyclone preheater connected in sequence; a cyclone-type dual-temperature zone calcination reactor, including a reactor cylinder, a spiral guide plate, and an adjustable baffle, wherein the reactor cylinder is provided with a first temperature zone, a transition zone, and a second temperature zone in sequence along its length, the spiral guide plate is disposed on the inner wall of the reactor cylinder to make the material flow in a spiral manner, and the adjustable baffle is disposed between the first temperature zone and the transition zone, and between the transition zone and the second temperature zone, for adjusting the material flow rate and residence time; and a pulse heating and magnetic field auxiliary system, including a pulse heating controller, an electric heating element array, a magnetic field generating device, and a cooling system, wherein the pulse heating controller is electrically connected to the electric heating element array to control the periodic fluctuation of the temperature in the first temperature zone, and the magnetic field generating device includes multiple sets of electromagnetic coils distributed along the circumference of the first temperature zone, each set of electromagnetic coils being energized by... The reactor is independently powered by a frequency converter, generating an alternating magnetic field with a gradient distribution along the axial direction. The cooling system is connected to the electromagnetic coil to maintain its operating temperature. The temperature control and atmosphere conditioning system includes a temperature acquisition module, a CO2 concentration monitoring module, an atmosphere conditioning module, and a central controller. Multiple temperature sensors from the temperature acquisition module are distributed in each temperature zone of the reactor. Multiple CO2 sensors from the CO2 concentration monitoring module are distributed at the inlet and outlet positions of the first and second temperature zones. The atmosphere conditioning module includes a flow meter, a regulating valve, and a fan. The central controller receives signals from the temperature acquisition module and the CO2 concentration monitoring module and outputs control commands to the pulse heating controller, the magnetic field generator, and the atmosphere conditioning module. The rapid cooling and product collection unit includes a cooler, a screening machine, and a product storage tank connected in series. The cooler inlet is connected to the outlet of the second temperature zone of the reactor, the cooler outlet is connected to the inlet of the screening machine, and the screening machine outlet is connected to the product storage tank.

[0014] In a preferred embodiment, the swirl-type dual-temperature zone calcination reactor is equipped with: a spiral guide plate made of metal sheet, which is spirally welded or fixed to the inner wall of the reactor cylinder; the spiral guide plate has a pitch of 0.8-1.2m and a lead angle of 15-25°, with 3-5 complete spiral turns along the axial direction; and an adjustable baffle made of heat-resistant alloy plate, driven by a hydraulic or electric push rod. One end of the push rod is fixed to the outer wall of the reactor, and the other end is connected to the baffle. The baffle can extend and retract in the radial direction of the reactor to adjust the cross-sectional area of ​​the channel. The extension and retraction stroke of the push rod is controlled by a central controller based on the material flow rate and CO2 concentration signal.

[0015] The pulse heating and magnetic field-assisted system includes: an electric heating element array comprising multiple heating elements distributed along the circumference and axial direction of the first temperature zone, the axial direction being divided into an inlet layer, an intermediate layer, and an outlet layer, with each layer's heating elements independently grouped, and each group's power independently controlled by a pulse heating controller; multiple sets of electromagnetic coils in the magnetic field generating device divided into three sections along the axial direction of the first temperature zone, each section containing 2-4 sets of electromagnetic coils, each section's electromagnetic coils connected to an independent frequency converter, the frequency converter being controlled by a central controller, outputting alternating currents of different intensities and frequencies, causing each section to generate magnetic fields of different intensities and frequencies; and a cooling system including cooling water pipes and a circulating pump, the inlet and outlet of the cooling water pipes being connected to the cooling jacket of the electromagnetic coil housing, and the circulating pump driving the cooling water to circulate in the pipes.

[0016] In a preferred embodiment, the temperature acquisition module of the temperature control and atmosphere conditioning system includes 16-24 thermocouple temperature sensors, with 6-8 sensors in the first temperature zone, 2-4 in the transition zone, and 8-12 in the second temperature zone. The signal terminals of each sensor are connected to the data acquisition card of the central controller via compensating wires. The CO2 concentration monitoring module includes 8-12 infrared CO2 sensors, with 2-3 sensors each at the inlet, middle, and outlet of the first temperature zone, and 2-3 at the outlet of the second temperature zone. Each sensor is mounted on a sampling probe that extends into the reactor. A sampling pump draws flue gas into the sensor measurement chamber, and the sensor output signal is connected to the central controller. In the atmosphere conditioning module, a flow meter is installed on the gas inlet pipe, a regulating valve is installed downstream of the flow meter, and a fan is installed at the tail of the reactor. The signal output terminal of the flow meter and the regulating valve are connected to the central controller. All valve control inputs are connected to the central controller, and the blower is connected to the central controller via a frequency converter. The central controller adopts an industrial computer and PLC architecture. The industrial computer runs control software, and the PLC performs real-time control. The industrial computer and PLC are connected via a communication interface. The input of the PLC is connected to the signals of each sensor, and the output is connected to each actuator. In the raw material pretreatment unit, the cobalt salt spraying device includes a solution storage tank, a metering pump, atomizing nozzles, and a spraying controller. The solution storage tank is connected to the inlet of the metering pump via a pipeline, and the outlet of the metering pump is connected to the atomizing nozzles via a pipeline. The atomizing nozzles are set on the conveying channel between the screening machine and the preheater, with 3-6 atomizing nozzles arranged along the circumference of the conveying channel. The spraying controller is connected to the central controller, receives material flow signals, calculates the amount of cobalt salt added, outputs control commands to the metering pump, and adjusts the flow rate of the metering pump.

[0017] In a preferred embodiment, the rapid cooling and product collection unit comprises: a vertical cooling tower with multiple layers of cooling plates inside, forming a material descent channel between the cooling plates; cooling plates connected to cooling water pipes or a cooling fan; a discharge device at the bottom of the cooler connected to the feed inlet of the screening machine; a multi-layer vibrating screen comprising a first screen, a second screen, and a third screen arranged sequentially, the first screen having a 1mm aperture, the second screen having a 3mm aperture, and the third screen having a 5mm aperture, with corresponding discharge ports below each screen; and a sealed product storage tank with a feed inlet and a protective gas interface at the top, and a discharge valve at the bottom, the feed inlet connected to the discharge ports of the screening machine via pipes.

[0018] The beneficial effects achieved by this invention are as follows:

[0019] First, this invention employs a dual-temperature-zone gradient calcination process. By combining pulsed pre-decomposition in the first temperature zone with complete decomposition in the second temperature zone, it achieves precise control and optimization of the magnesite decomposition process. The dual-temperature-zone design avoids the uneven decomposition problem caused by the single temperature in traditional single-temperature-zone calcination. The first temperature zone (650-750℃) achieves pre-decomposition of magnesite, creating a good structural foundation for subsequent complete decomposition. The second temperature zone (850-950℃) ensures the complete decomposition of the remaining magnesium carbonate. This staged temperature control strategy allows magnesite to undergo different physicochemical changes at different temperatures, effectively preventing premature surface sintering that hinders internal decomposition and ensuring the full progress of the decomposition reaction, thereby obtaining a high-purity, highly active magnesium oxide product.

[0020] Secondly, this invention introduces pulsed heating technology and alternating magnetic field-assisted technology. Pulsed heating generates alternating thermal stress within the magnesite particles by periodically fluctuating the temperature of the first temperature zone within a range of ±20-40℃ from the reference temperature. This promotes the formation of microcrack channels in the crystal structure, which facilitates CO2 escape, thus avoiding the problem of a dense surface layer hindering internal decomposition that may occur with isothermal heating. Simultaneously, the applied gradient alternating magnetic field gradually increases from 0.02-0.03T at the inlet to 0.06-0.08T at the outlet, with the magnetic field frequency correspondingly increasing from 10-20Hz to 40-50Hz. This gradient magnetic field design causes the material to undergo three stages during its movement: pre-decomposition, crystal orientation, and lattice rearrangement. The electromagnetic effect induced by the magnetic field promotes ion migration and gas escape, while also influencing the orientation growth of newly formed magnesia crystals, resulting in a porous and loose structure with more active sites and a larger specific surface area.

[0021] Third, this invention sets up a CO2 concentration monitoring system with 3-5 monitoring points in the first temperature zone to collect data in real time. By calculating the deviation between the weighted average concentration and the target concentration, the residence time is dynamically adjusted. When the CO2 concentration is too high, the residence time is extended to ensure full decomposition; when the concentration is too low, the residence time is shortened to improve efficiency. Feedback control ensures that the decomposition process is always in the optimal state, avoiding problems of insufficient decomposition or over-processing. The swirl reactor designed in this invention adopts a spiral guide plate design, which makes the material flow in a spiral within the reactor, extending the residence time and improving the heat and mass transfer effect. The pulse heating system achieves precise temperature fluctuation through the layered grouping control of the electric heating element array. The magnetic field generating device adopts multiple sets of electromagnetic coils arranged in segments along the axial direction. The independent frequency conversion power supply control of each segment allows the magnetic field strength and frequency to be gradient adjusted according to process requirements. The cooling system ensures that the electromagnetic coils maintain a stable operating temperature during long-term operation, guaranteeing the precise execution and stable operation of complex processes.

[0022] Fourth, the temperature control and atmosphere conditioning system, as well as the rapid cooling and product collection unit of this invention, achieve automated control of the production process and further optimization of product quality. The control system employs a multi-point monitoring network consisting of 16-24 thermocouple temperature sensors and 8-12 infrared CO2 sensors, combined with an industrial computer and PLC control architecture, to achieve real-time monitoring of temperature and atmosphere composition and precise adjustment using PID control algorithms, ensuring the stability of temperature in each temperature zone and the optimization of atmosphere conditions. The rapid cooling unit rapidly cools high-temperature magnesium oxide to below 200℃ at a cooling rate of 20-50℃ / min. This rapid cooling process effectively fixes the porous and loose crystal structure formed at high temperatures, preventing further grain growth and pore closure during slow cooling, thus maintaining the product's high activity and large specific surface area characteristics. The multi-layer vibrating sieving system enables automatic classification and collection of products with different particle sizes, meeting the differentiated requirements of particle size distribution in different application fields. Attached Figure Description

[0023] Figure 1 This is a comparison chart of the activity of magnesium oxide between Examples 1 to 4 and Comparative Examples 1 to 4. Figure 1 Neutron graph a is a bar chart comparing the activity of all 8 samples, and subgraph b is a comparison of the activity of Example 1 and Comparative Example 1.

[0024] Figure 2 This is a comparison chart of the specific surface area of ​​magnesium oxide between Examples 1 to 4 and Comparative Examples 1 to 4. Figure 2 Neutron plot a is a bar chart comparing the specific surface area of ​​all 8 samples, and subplot b is a comparison chart of the specific surface area of ​​Example 3 and Comparative Example 1.

[0025] Figure 3This is a line graph comparing Examples 1 to 4 with Comparative Examples 1 to 4 regarding three key indicators: activity, specific surface area, and iodine adsorption value.

[0026] Figure 4 This is a comparison chart of the average particle size of magnesium oxide between Examples 1 to 4 and Comparative Examples 1 to 4. Figure 4 Neutron plot a is a columnar comparison of the average particle size of all 8 samples, and subplot b is a comparison of the average particle size of the example and the average particle size of the comparative example.

[0027] Figure 5 This is a scatter plot comparing the iodine adsorption values ​​of Examples 1 to 4 and Comparative Examples 1 to 4.

[0028] Figure 6 This is a graph analyzing the effect of calcination temperature parameters on the properties of magnesium oxide. Figure 6 Subplot a shows the effect of temperature in the first temperature zone on activity; subplot b shows the effect of temperature in the second temperature zone on activity; subplot c shows the effect of temperature in the first temperature zone on relative surface area; and subplot d shows the effect of temperature in the second temperature zone on relative surface area.

[0029] Figure 7 This is a heatmap showing the comprehensive performance evaluation of Examples 1 to 4 and Comparative Examples 1 to 4.

[0030] Figure 8 This is a flowchart of the method for preparing highly active magnesium oxide by dual-temperature gradient calcination of magnesite according to the present invention.

[0031] Figure 9 This is a structural diagram of the system for preparing highly active magnesium oxide by dual-temperature gradient calcination of magnesite according to the present invention. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Reference Figures 8-9This invention provides a detailed description of a method and system for preparing highly active magnesium oxide using a dual-temperature-zone gradient calcination process for magnesite. The invention employs a dual-temperature-zone gradient calcination process, combined with pulse heating and magnetic field-assisted technology, to achieve precise control of the magnesite decomposition process, thereby producing a highly active magnesium oxide product. The method for preparing highly active magnesium oxide using a dual-temperature-zone gradient calcination process for magnesite includes five main steps: raw material pretreatment, pulsed pre-decomposition in the first temperature zone, heating in the transition zone, complete decomposition in the second temperature zone, and cooling and collection.

[0034] In the S1 raw material pretreatment step, the magnesite raw material is first crushed. The purpose of crushing is to increase the specific surface area of ​​the magnesite particles, creating favorable conditions for subsequent calcination and decomposition. The particle size of the crushed magnesite is controlled within a suitable range; excessively large particle sizes will lead to uneven heat transfer and incomplete decomposition, while excessively small particle sizes will easily cause dust to fly and equipment blockage. The crushed magnesite is then sent to a preheating device for preheating treatment. The preheating temperature is set based on the thermal decomposition characteristics of magnesite and the requirements of subsequent processes. The preheating process removes surface moisture from the magnesite, increases the particle temperature, and prepares it for entering the first temperature zone. At the same time, preheating also reduces energy consumption in the subsequent calcination process.

[0035] In step S1, a cobalt salt solution is sprayed onto the surface of the magnesite before preheating. The amount of cobalt salt added is calculated using the following formula: ;in, Indicates the mass of cobalt in the cobalt salt (unit: g); The mass of magnesite raw material is expressed in kg; α represents the cobalt doping coefficient, a dimensionless parameter. The conversion factor is dimensionless. Spraying is achieved through atomizing nozzles; atomization technology ensures the cobalt salt solution is uniformly distributed on the surface of magnesite particles in the form of fine droplets. Simultaneous stirring or agitation ensures each particle comes into contact with the cobalt salt solution, avoiding localized excessively high or low concentrations. The design of immediately transferring the solution to a preheating device after spraying prevents uneven distribution or loss of the cobalt salt solution at room temperature. During preheating, the cobalt salt solution evaporates, and cobalt ions adhere to the surface of the magnesite particles through adsorption or chemical bonding, forming a cobalt-doped precursor structure.

[0036] Introducing trace amounts of cobalt ions during the calcination of magnesite forms a Co-Mg-O solid solution structure at high temperatures. The cobalt ion doping influences the growth pattern of MgO crystals, promoting the formation of more surface defects and active sites, thus improving the overall activity of magnesium oxide. Traditional magnesium oxide adsorbs various metal ions indiscriminately; however, cobalt doping increases the selectivity of magnesium oxide for cobalt ions by 2-3 times. If used in cobalt extraction processes, this can reduce the co-adsorption of other impurity metals, improve cobalt recovery, and reduce the difficulty of subsequent separation and purification.

[0037] In the S2 first-temperature zone pulsed pre-decomposition process, preheated magnesite is fed into the first temperature zone for pulsed heating treatment. The temperature range of the first temperature zone is selected based on the initial decomposition temperature of magnesite and to avoid over-decomposition. Pulsed heating refers to a heating method in which the temperature fluctuates periodically around a set reference value, offering unique advantages compared to traditional isothermal heating. Pulsed heating generates alternating thermal stress within the magnesite particles, promoting the formation of microcracks in the crystal structure, thus... The escape of gas creates pathways while preventing the formation of a surface sintered layer that hinders internal decomposition. Controlling the temperature fluctuation range is crucial; too small a fluctuation will fail to generate effective thermal stress, while too large a fluctuation may cause particle breakage and thermal shock to the equipment.

[0038] In the specific operation of pulse temperature control, the reference temperature of the first temperature zone is set. As the center value for temperature control. Actual temperature. exist Fluctuations within a range, of which Indicates the amplitude of temperature fluctuation (unit: °C). Temperature fluctuation period. With pulse frequency The relationship between them is determined by the formula: ;in, Indicates the temperature fluctuation period (unit: s); This represents the pulse frequency (unit: Hz); the formula reflects the reciprocal relationship between period and frequency. The selection of the pulse frequency needs to consider the thermal response time and decomposition kinetics of the magnesite particles. If the frequency is too high, the internal temperature of the particles will not have enough time to respond; if the frequency is too low, the pulse effect will be insignificant.

[0039] The application of an alternating magnetic field is another important technical feature of the first temperature zone. The mechanism by which the magnetic field affects the decomposition process of magnesite lies in its influence on ion migration and crystal orientation, thus promoting the decomposition reaction. Compared to a constant magnetic field, an alternating magnetic field has a stronger activation effect, generating eddies and thermal effects within the magnesite particles, thereby improving decomposition efficiency. The magnetic field gradient control technology divides the first temperature zone into three segments along its length, applying magnetic fields of different intensities and frequencies to each segment to create a gradient distribution. The magnetic field strength at the inlet segment... and frequency The magnetic field strength is relatively low, mainly playing a preliminary activation role; the magnetic field strength in the middle section is... and frequency Moderate, undergoing the main pre-decomposition process; magnetic field strength at the exit section and frequency At its highest point, the pre-decomposition process is complete. The length ratio of each segment is designed based on the residence time requirements of the material at different decomposition stages; the middle segment is longer because the main decomposition process requires more time. Smooth transitions between adjacent segments avoid the adverse effects of sudden magnetic field changes on the decomposition process. The concentration feedback control system enables real-time monitoring and dynamic adjustment of the decomposition process. Multiple [systems / mechanisms] are set along the material flow direction in the first temperature zone. Concentration monitoring points reflect the degree of decomposition at different locations. The number of monitoring points is selected based on the temperature range length and monitoring accuracy requirements; too few monitoring points will fail to accurately reflect the decomposition state, while too many monitoring points will increase system complexity and cost. Weighted average concentration. The calculation takes into account the importance of each monitoring point location, reflecting the average decomposition level of the entire temperature range. The calculated residence time after adjustment uses the following formula: ;in, Indicates the adjusted dwell time (unit: min); Indicates the baseline dwell time (unit: min); This represents the adjustment coefficient, a dimensionless parameter. Indicates weighted average Concentration (unit: %) Indicate target Concentration (unit: %); This formula reflects the relationship between residence time and... Linear relationship of concentration deviation. Adjustment coefficient. The value of affects the response sensitivity of the control system; a value that is too large can easily cause oscillations, while a value that is too small will result in a slow response. When When the concentration is abnormal, corresponding adjustment measures are taken. When the weighted average concentration exceeds the upper limit, it indicates insufficient decomposition, and the residence time needs to be extended, which can be achieved by reducing the material conveying rate or increasing the baffle opening. When the weighted average concentration is below the lower limit, it indicates excessive decomposition or excessive efficiency, and the residence time needs to be shortened, which can be achieved by increasing the material conveying rate or decreasing the baffle opening. The feedback adjustment mechanism ensures that the pre-decomposition effect in the first temperature zone is stable and controllable. During the processing in the first temperature zone, the material undergoes three stages under the combined action of pulsed temperature and gradient magnetic field: pre-decomposition, crystal orientation, and lattice rearrangement. The pre-decomposition stage mainly involves the decomposition of magnesium carbonate on the surface and in the shallow layer, releasing... The process involves three stages: gas formation, crystal orientation (where newly formed magnesium oxide crystals align under the influence of a magnetic field), and lattice rearrangement (where the crystal structure is further optimized, resulting in a highly active magnesium oxide structure). Successful completion of these three stages lays the foundation for the preparation of highly active magnesium oxide.

[0040] The S3 transition zone heating step connects the first and second temperature zones, serving as a temperature transition and connection. It controls the material outlet temperature from the first temperature zone. Linear heating to the inlet temperature of the second temperature zone The purpose of linear heating is to avoid the adverse effects of sudden temperature changes on product quality. Heating rate. The calculation uses the following formula: ;in, Indicates the heating rate (unit: °C / min); Indicates the inlet temperature of the second temperature zone (unit: °C); This indicates the outlet temperature of the first temperature zone (unit: °C). The transition time is expressed in minutes; this formula illustrates the relationship between the heating rate, temperature difference, and time. Controlling the heating rate is crucial; an excessively rapid heating rate may lead to product instability, while an excessively slow heating rate will negatively impact production efficiency.

[0041] Maintaining appropriate atmosphere flow during heating, with the flow rate increasing with temperature, is based on the physical principle that gas molecule motion intensifies at high temperatures. Appropriate atmosphere flow promptly removes residual gases. Gases are used to prevent the products from recarbonizing at high temperatures, as recarbonization reduces the activity and purity of magnesium oxide. The atmosphere flow rate needs to be adjusted in coordination with the heating rate to ensure that the gases produced during decomposition are effectively removed throughout the transition process.

[0042] The S4 second-zone complete decomposition step achieves the complete decomposition of magnesite. The temperature in the second zone is higher than in the first zone; at this temperature, the remaining magnesium carbonate in the magnesite is completely decomposed, ensuring high product purity. Temperature control employs a PID control algorithm, a classic feedback control method that achieves precise temperature control. The mathematical expression for the PID control algorithm is: ;in, This indicates the adjusted heating power (unit: kW). Indicates the reference heating power (unit: kW); Represents the proportionality constant, a dimensionless parameter; Integral coefficient (unit: min) -1 ); Represents the differential coefficient (unit: min); The term represents the temperature deviation (unit: °C); the proportional term reflects the magnitude of the current deviation, the integral term eliminates the steady-state deviation, and the derivative term predicts the trend of deviation change. The three terms work together to achieve precise control.

[0043] Second temperature zone The concentration dynamic regulation mechanism monitors the outlet. Concentration is used to determine the completeness of decomposition. The adjusted formula is: ;

[0044] in, Indicates the adjusted dwell time (unit: min); Indicates the baseline dwell time (unit: min); This represents an adjustment coefficient, a dimensionless parameter. Indicates export Concentration (unit: %) Indicates reference concentration (unit: %); This represents a logarithmic function with base 10, dimensionless. The introduction of the logarithmic function makes the adjustment response more sensitive in the low-concentration region and relatively flat in the high-concentration region; the nonlinear response characteristics conform to the kinetic laws of the decomposition process. When the outlet... When the concentration is higher than the reference concentration, the residence time is correspondingly prolonged; when the outlet... When the concentration is lower than the reference concentration, the residence time should be appropriately shortened to ensure a balance between the integrity and efficiency of decomposition.

[0045] The S5 cooling and collection step completes the final product preparation. The high-temperature magnesium oxide from the second temperature zone outlet is fed into a cooling device for rapid cooling. The cooling method can be either indirect water cooling or forced air cooling. Indirect water cooling has the advantages of high cooling efficiency and precise temperature control, but the equipment is more complex; forced air cooling has the advantages of simple structure and convenient operation, but the cooling efficiency is relatively low. Cooling rate The calculation uses the following formula: ;in, Indicates the cooling rate (unit: °C / min); Indicates the inlet temperature of the cooler (unit: °C); Indicates the cooler outlet temperature (unit: °C); The formula represents the cooling time (in minutes); it reflects the linear relationship between the cooling rate and the temperature difference and time.

[0046] Rapid cooling helps to stabilize the crystal structure of magnesium oxide, preventing grain growth and reduced activity during slow cooling. The cooling rate is controlled by adjusting the flow rate of the cooling medium; a higher flow rate results in a faster cooling rate, while a lower flow rate results in a slower cooling rate. The purpose of introducing a protective gas during cooling is to prevent magnesium oxide from absorbing moisture, as it is highly hygroscopic and readily reacts with moisture in the air at high temperatures to form magnesium hydroxide, which affects product quality. Dry, inert gases such as nitrogen or argon are typically chosen as the protective gas.

[0047] After cooling, magnesium oxide is graded using a vibrating screen to separate products of different particle sizes. The vibrating screen utilizes high-frequency vibration of the screen surface to separate particles of different sizes; smaller particles pass through the screen openings, while larger particles remain on the screen surface. Different particle size grades have different applications and market values; fine-grained products are typically used in high-end applications, while coarse-grained products are used for general industrial applications.

[0048] This invention also designs a system for preparing highly active magnesium oxide by dual-temperature zone gradient calcination of magnesite, including a raw material pretreatment unit, a cyclone dual-temperature zone calcination reactor, a pulse heating and magnetic field-assisted system, a temperature control and atmosphere conditioning system, and a rapid cooling and product collection unit. The raw material pretreatment unit includes a crusher, a screening machine, a cobalt salt spraying device, and a cyclone preheater connected in sequence. The crusher is responsible for crushing large pieces of magnesite to a suitable particle size. The crusher can be a jaw crusher, cone crusher, or impact crusher, determined according to processing capacity and product requirements. The screening machine classifies the crushed material by particle size. The oversize material is returned to the crusher for further crushing, while the undersize material enters the next process, ensuring that the particle size of the material entering subsequent processes meets the requirements. The cobalt salt spraying device achieves uniform spraying of the cobalt salt solution, including a solution storage tank, a metering pump, atomizing nozzles, and a spray controller. These components work together to achieve precise cobalt salt addition. The cyclone preheater utilizes heat exchange between high-temperature gas and the material for preheating. The cyclone separation design achieves heat exchange while avoiding dust dispersion.

[0049] The swirl-type dual-temperature-zone calcination reactor is the core equipment of the system. Its swirl design causes the material to flow in a spiral pattern within the reactor, extending residence time and improving heat and mass transfer efficiency. The reactor shell is sequentially divided into a first temperature zone, a transition zone, and a second temperature zone along its length, each with different temperature regimes and control requirements. Spiral guide vanes are installed on the inner wall of the reactor shell to guide the material in a spiral flow; the pitch and lead angle of the guide vanes affect the flow state and residence time distribution of the material. Adjustable baffles are installed between the temperature zones, controlling the material flow rate and residence time by adjusting the cross-sectional area of ​​the channels. The adjustment of the baffles is executed by the automatic control system based on process parameters.

[0050] The pulse heating and magnetic field-assisted system achieves specialized heating and magnetic field treatment of the first temperature zone. The pulse heating controller controls the power output of the heating element array according to a preset program, achieving periodic temperature fluctuations. The heating element array is distributed along the circumference and axis of the first temperature zone, ensuring heating uniformity and control flexibility. The magnetic field generating device includes multiple sets of electromagnetic coils distributed along the first temperature zone. Each set of electromagnetic coils is powered by an independent frequency converter, generating the required gradient magnetic field. A cooling system is connected to the electromagnetic coils to prevent overheating, which could affect magnetic field stability and equipment lifespan.

[0051] The temperature control and atmosphere conditioning system enables automatic control of the entire calcination process. Multiple temperature sensors from the temperature acquisition module are distributed in various temperature zones of the reactor to monitor the temperature distribution in real time. Multiple concentration monitoring modules Sensors are distributed in key locations to monitor the progress of the decomposition process. The atmosphere control module includes flow meters, regulating valves, and fans to control the flow rate and composition of the atmosphere. The central controller, acting as the "brain" of the system, receives signals from various sensors, runs control algorithms, and outputs control commands to achieve coordinated operation of the entire system.

[0052] The spiral guide vane is made of sheet metal, specifically high-temperature and corrosion-resistant alloy steel. Its spiral structure is installed on the inner wall of the reactor via welding or mechanical fixing. The geometric parameters of the spiral guide vane, such as pitch and lead angle, directly affect the flow characteristics of the material. A larger pitch results in faster axial movement of the material, while a smaller pitch leads to better radial mixing. The lead angle affects the rotational intensity and centrifugal force of the material; a balance must be found between mixing efficiency and energy consumption.

[0053] The adjustable baffle is made of heat-resistant alloy plate, which can withstand thermal shock and corrosion in high-temperature environments. The baffle is driven by either a hydraulic or electric actuator, and the choice of actuator is based on the requirements of adjustment accuracy, response speed, and reliability. Hydraulic actuators have the advantages of large output force and precise positioning, but the system is more complex; electric actuators have the advantages of simple control and convenient maintenance, but the output force is relatively small. One end of the actuator is fixed to a bracket on the outer wall of the reactor, and the other end is connected to the baffle, realizing the radial extension and retraction of the baffle.

[0054] The design of the heating element array takes into account both heating uniformity and control flexibility. Multiple heating elements distributed circumferentially ensure circumferential temperature uniformity, while the multi-layered design along the axial direction enables zoned control. Independent control of the inlet, middle, and outlet layers allows temperature distribution to be adjusted according to process requirements. Each group of heating elements has its power independently controlled by a pulse heating controller, which adjusts the timing of the heating power according to a set pulse waveform.

[0055] The electromagnetic coils in the magnetic field generator are divided into three sections along the axial direction of the first temperature zone. Each section contains multiple sets of electromagnetic coils, forming a gradient magnetic field distribution. The design of the electromagnetic coils needs to consider factors such as magnetic field strength, magnetic field uniformity, and energy consumption. Each section of the electromagnetic coils is connected to an independent frequency converter, which outputs alternating current of different frequencies and intensities to achieve flexible adjustment of the magnetic field parameters. The frequency converter is controlled by a central controller, which automatically adjusts the output parameters according to process requirements and feedback signals.

[0056] The cooling system includes cooling water piping and a circulating pump to provide effective heat dissipation for the electromagnetic coil. The inlet and outlet of the cooling water piping are connected to the cooling jacket of the electromagnetic coil housing, forming a closed-loop circulation system. The circulating pump drives the cooling water to circulate within the piping, carrying away the heat generated by the electromagnetic coil and maintaining it at a suitable operating temperature. The flow rate and temperature of the cooling water need to be adjusted according to the power of the electromagnetic coil and the ambient temperature.

[0057] The temperature acquisition module includes a reasonable number of thermocouple temperature sensors. The number and location of the sensors are based on the accuracy requirements and economic considerations for temperature monitoring. The allocation of sensors in the first temperature zone, transition zone, and second temperature zone reflects the importance and control accuracy requirements of each zone. The signal terminals of each sensor are connected to the data acquisition card of the central controller via compensating wires. The purpose of the compensating wires is to reduce the impact of wire resistance on measurement accuracy. The concentration monitoring module uses infrared. The sensor enables online monitoring of gas concentration. Infrared sensors offer advantages such as fast response, high accuracy, and good stability, making them suitable for gas monitoring in high-temperature environments. The sensor is mounted on a sampling probe that extends deep into the reactor to ensure the collection of a representative gas sample. A sampling pump draws the flue gas into the sensor's measurement chamber, overcoming the influence of pressure and temperature inside the reactor on the measurement.

[0058] The atmosphere control module utilizes a flow meter, regulating valve, and fan to work together to control atmospheric conditions. The flow meter is installed on the gas inlet line to monitor the inlet flow rate in real time; the regulating valve is installed downstream of the flow meter to adjust the gas flow rate according to control commands; and the fan is installed at the reactor tail to provide power for the atmosphere flow. The signal and control interfaces of each device are connected to a central controller for unified and coordinated control.

[0059] The central controller adopts a hierarchical control architecture of industrial PC and PLC. The industrial PC is responsible for running the control software, human-machine interface, and data management, while the PLC is responsible for executing real-time control tasks. This architecture combines the computing power of the industrial PC with the real-time performance of the PLC, improving the system's reliability and maintainability. The industrial PC and PLC are connected via a standard communication interface to achieve data exchange and command transmission.

[0060] The cobalt salt spraying system is designed to ensure precise addition and uniform distribution of the cobalt salt solution. The solution storage tank, made of corrosion-resistant stainless steel or polymer material, stores the prepared cobalt salt solution. A metering pump precisely measures the amount of cobalt salt solution needed based on the material flow rate and the set cobalt salt addition ratio. Atomizing nozzles atomize the cobalt salt solution into fine droplets, improving contact efficiency with the magnesite particles. The spraying controller communicates with a central controller, receiving material flow signals and automatically calculating the amount of cobalt salt to be added.

[0061] The rapid cooling and product collection unit achieves the cooling, grading, and collection of the final product. The cooler employs a vertical cooling tower design, with multiple layers of cooling plates inside the tower to increase the heat transfer area and improve cooling efficiency. The material descent channels formed between the cooling plates provide a path for material flow, allowing heat exchange between the material and the cooling medium during its descent. The cooling plates can be connected to cooling water pipes for water cooling or to air coolers for air cooling, allowing for the selection of the appropriate cooling method based on specific conditions.

[0062] The screening machine employs a multi-layer vibrating screen design to separate products of different particle sizes. The vibrating screen utilizes the reciprocating vibration of the screen box to throw the material onto the screen surface, allowing particles of different sizes to be classified by passing through corresponding screen openings. The apertures of the first, second, and third screens gradually increase, achieving classification from fine to coarse. Each screen has a corresponding discharge port below it to collect products of different particle sizes.

[0063] The product storage tank is designed as a sealed container to prevent the product from absorbing moisture and becoming contaminated. The top inlet connects to the screening machine's outlet via pipeline, while the bottom discharge valve is used for bagging or loading the product. A protective gas inlet allows for the introduction of dry protective gas into the tank to maintain a dry environment inside.

[0064] Example 1 provides a specific application case of preparing highly active magnesia using dual-temperature zone gradient calcination of magnesite. This case addresses the high-activity magnesia preparation needs of a refractory material production enterprise, employing the method and system described in this invention for industrial production. This enterprise mainly produces high-end refractory materials and has high requirements for the activity of magnesia, requiring the citric acid method activity of the magnesia product to be no less than 140s and the specific surface area to reach 25m². 2 / g or more. The system used in this embodiment includes a raw material pretreatment unit, a swirling dual-temperature zone calcination reactor, a pulse heating and magnetic field-assisted system, a temperature control and atmosphere conditioning system, and a rapid cooling and product collection unit. The parameters of each unit are configured and debugged according to the technical solution of this invention.

[0065] In step S1, magnesite from a certain region is selected as raw material. This magnesite contains 92.5% magnesium carbonate and has a low impurity content. First, the magnesite raw material is fed into a jaw crusher for crushing. After crushing, it is screened by a vibrating screen. The oversize material is returned to the crusher for further crushing, while the undersize material has a particle size controlled at approximately 5 mm. The crushed magnesite is then fed into a cobalt salt spraying device, where a 0.5 mol / L cobalt nitrate solution is sprayed. The cobalt doping coefficient α is set to 5.5, calculating that 0.55 g of cobalt nitrate solution containing cobalt is required per 100 kg of magnesite. During spraying, a material stirring device is simultaneously activated to ensure that the cobalt salt solution is evenly distributed on the surface of the magnesite particles. After spraying, the material is immediately fed into a cyclone preheater. The preheating temperature is set to 250℃, and the preheating time is approximately 10 minutes. During preheating, the water in the cobalt nitrate solution evaporates, the cobalt nitrate undergoes thermal decomposition, and cobalt ions adhere to the surface of the magnesite particles, forming a cobalt-doped precursor structure.

[0066] In step S2, the preheated magnesite is fed into the first temperature zone of a cyclone-type dual-temperature zone calcination reactor. The reference temperature of the first temperature zone is set at 700℃, and the temperature fluctuation range is set at ±30℃, meaning the actual temperature fluctuates periodically within the range of 670℃ to 730℃. The pulse frequency is set to 0.05Hz, and the temperature fluctuation period is calculated to be 20s according to the formula. Pulse heating is achieved through an array of electric heating elements, which are divided into three groups: an inlet layer, an intermediate layer, and an outlet layer. The power of each group is independently controlled, and the heating power is periodically adjusted according to the set waveform by a pulse heating controller. Four carbon dioxide concentration monitoring points are set along the material flow direction in the first temperature zone, located at the inlet, one-third, two-thirds, and outlet positions, respectively. The carbon dioxide concentration values ​​of each monitoring point are collected in real time, and the weighted average carbon dioxide concentration is calculated using a weighted average algorithm. The weighting coefficients for the inlet, intermediate two points, and outlet are set to 0.2, 0.3, 0.3, and 0.2, respectively. Based on the deviation of the weighted average carbon dioxide concentration from the target concentration of 6%, the adjusted residence time is calculated using an adjustment formula. The baseline residence time was set to 20 minutes, with an adjustment coefficient of 0.2. Throughout the first temperature zone processing, the actual residence time was controlled near the set value by adjusting the opening of the adjustable baffle and the material conveying rate, ensuring stable pre-decomposition results.

[0067] Simultaneously with step S2, the alternating magnetic field system is activated. The first temperature zone is divided axially into an inlet section, a middle section, and an outlet section, with a length ratio of 1:1.5:1. The inlet section is 0.8 m long, the middle section is 1.2 m long, and the outlet section is 0.8 m long. The applied magnetic field strength is 0.025 T with a frequency of 15 Hz in the inlet section; 0.05 T with a frequency of 30 Hz in the middle section; and 0.07 T with a frequency of 45 Hz in the outlet section. Each section's magnetic field is controlled by an independent frequency converter, with a smooth transition in magnetic field strength and frequency between adjacent sections, and a transition zone length of 0.4 m. Under the combined action of pulsed temperature and gradient magnetic field, the material undergoes three stages in the first temperature zone: pre-decomposition, crystal orientation, and lattice rearrangement, promoting carbon dioxide escape and directional growth of magnesia crystals. Monitoring data shows that the carbon dioxide concentration at the outlet of the first temperature zone is approximately 12%, indicating that the magnesite has completed partial decomposition.

[0068] In step S3, the material enters the transition zone from the outlet of the first temperature zone. The outlet temperature of the first temperature zone is 730℃, the inlet temperature of the second temperature zone is set to 865℃, and the transition time is set to 7.5 min. Based on the heating rate calculation formula, the heating rate is controlled at 18℃ / min. Heating elements distributed axially are installed in the transition zone, and the heating power is adjusted using a PID control algorithm to ensure the material temperature increases linearly according to the set heating rate. Simultaneously, appropriate atmosphere flow is maintained in the transition zone, with the atmosphere velocity increasing from 1.2 m at the inlet as the temperature rises. 3The flow rate gradually increased to 1.8m at the outlet. 3 / h, promotes the timely removal of residual carbon dioxide and prevents the product from recarbonizing at high temperatures.

[0069] In step S4, the material enters the second temperature zone for complete decomposition. The temperature in the second temperature zone is constantly controlled at 900℃, and a PID control algorithm is used to adjust the heating power in real time to ensure temperature stability. The proportional gain of the PID controller is set to 1.2, the integral gain to 0.08 / min, and the derivative gain to 0.5min. Two carbon dioxide concentration sensors are installed at the outlet of the second temperature zone to monitor the outlet carbon dioxide concentration in real time. Based on the ratio of the outlet carbon dioxide concentration to a reference concentration of 3%, the material residence time is dynamically adjusted using a logarithmic function formula. The baseline residence time is set to 32min, and the adjustment coefficient is set to 0.25. During operation, the outlet carbon dioxide concentration stabilizes at around 2.5%, indicating that the magnesite has been completely decomposed. The actual residence time is controlled at around 33min to ensure the integrity of the decomposition.

[0070] In step S5, magnesium oxide with an outlet temperature of 900℃ in the second temperature zone is fed into a vertical cooling tower for rapid cooling. The cooling tower has five layers of cooling plates connected to cooling water pipes, employing an indirect water cooling method. The cooler outlet temperature is set to 200℃, and the cooling time is set to 20 minutes. Based on the cooling rate calculation formula, the cooling rate is controlled at 35℃ / min. The actual cooling rate is maintained near the set value by adjusting the cooling water flow rate. During the cooling process, dry nitrogen is introduced as a protective gas at a flow rate of 5 m³ / min. 3 / h, to prevent magnesium oxide from absorbing moisture. The cooled magnesium oxide is then fed into a multi-layer vibrating screen for sieving. The vibrating screen has three layers of screens with apertures of 1mm, 3mm, and 5mm, separating products into three particle size grades: less than 1mm, 1-3mm, and 3-5mm. The sieved products of each grade are collected in sealed product storage tanks, which are purged with dry nitrogen to maintain a dry environment.

[0071] Example 2 is based on Example 1, but differs in that crushed magnesite with a particle size of 7mm is used in the raw material pretreatment stage, and the preheating temperature is increased to 290℃. The cobalt doping coefficient α is set to the upper limit of 9, and a cobalt acetate solution containing 0.9g of cobalt is added per 100kg of magnesite. The reference temperature of the first temperature zone is increased to 745℃, the temperature fluctuation range is set to ±38℃, the pulse frequency is set to 0.04Hz, and the residence time is 24min. The heating rate of the transition zone is set to 14℃ / min, the temperature of the second temperature zone is increased to 940℃, and the residence time is 38min. The cooling rate is increased to 48℃ / min. Product test results show that the magnesium oxide activity is 142s and the specific surface area is 24.5m². 2The content of magnesium oxide is 98.5%, the average particle size is 2.2µm, and the iodine adsorption value is 128mg / g.

[0072] Example 3 differs from Example 1 in that the raw material is crushed to a particle size of 3.5 mm, and the preheating temperature is set to 210℃. The cobalt doping coefficient α is 1.5, and 0.15 g of cobalt nitrate solution containing cobalt is added per 100 kg of magnesite. The reference temperature for the first temperature zone is set to 660℃, with a temperature fluctuation range of ±22℃, a pulse frequency of 0.067 Hz, and a residence time of 16 min. The heating rate in the transition zone is 6℃ / min, and the temperature in the second temperature zone is set to 860℃ with a residence time of 26 min. The cooling rate is set to 22℃ / min. Product test results show that the magnesium oxide activity is 151 s and the specific surface area is 28.2 m². 2 The content of magnesium oxide is 97.8%, the average particle size is 1.5µm, and the iodine adsorption value is 142mg / g.

[0073] Example 4 differs from Example 1 in that the raw material particle size is 4.5 mm, the preheating temperature is 225℃, the cobalt doping coefficient α is 3.8, the first temperature zone reference temperature is 680℃, the temperature fluctuation range is ±28℃, the pulse frequency is 0.055Hz, and the residence time is 18 min. The transition zone heating rate is 10℃ / min, the second temperature zone temperature is 880℃, and the residence time is 29 min. The cooling rate is 30℃ / min. Product test results show that the magnesium oxide activity is 150s and the specific surface area is 27.5m². 2 The content of magnesium oxide is 98.0%, the average particle size is 1.6µm, and the iodine adsorption value is 138mg / g.

[0074] Comparative Example 1: Magnesium oxide was prepared using a traditional single-zone isothermal calcination method without pulse heating or magnetic field assistance. Magnesite raw material with a particle size of 5 mm was preheated to 250°C and then directly fed into a single-zone calcination furnace. The furnace temperature was maintained at a constant 850°C for 60 minutes. The calcined magnesium oxide was then cooled to 200°C using the same cooling method. Product testing results showed that the magnesium oxide had an activity of 108 s and a specific surface area of ​​18.5 m². 2 The magnesium oxide content was 97.2% (g), the average particle size was 3.8 µm, and the iodine adsorption value was 95 mg / g. Compared with the examples, the magnesium oxide prepared in Comparative Example 1 had significantly lower activity, smaller specific surface area, and coarser particle size.

[0075] Comparative Example 2 employed a dual-temperature gradient calcination method but did not use magnetic field-assisted technology. Other process parameters were the same as in Example 1: the first temperature zone used pulse heating with a reference temperature of 700℃, a temperature fluctuation range of ±30℃, and a residence time of 20 min; the second temperature zone was 900℃ with a residence time of 32 min; cobalt salt was added with a cobalt doping coefficient of 5.5. Product testing results showed that the magnesium oxide activity was 128 s and the specific surface area was 21.8 m². 2 The sample contained 97.9% magnesium oxide, had an average particle size of 2.5 µm, and an iodine adsorption value of 115 mg / g. Compared with Example 1, all indicators of Comparative Example 2 decreased.

[0076] Comparative Example 3 employed a dual-temperature-zone gradient calcination method, but instead of pulse heating, a constant-temperature heating method was used in the first temperature zone. The first temperature zone was maintained at 700℃ for 20 minutes, and other parameters, including magnetic field assistance, were the same as in Example 1. Product test results showed that the magnesium oxide activity was 132s and the specific surface area was 22.5m². 2 The sample contained 98.0% magnesium oxide, had an average particle size of 2.3 µm, and an iodine adsorption value of 118 mg / g. Compared to Example 1, Comparative Example 3 showed a decrease in activity and specific surface area.

[0077] Comparative Example 4 employed a dual-temperature-zone gradient calcination method, using pulse heating and magnetic field-assisted technology, but without the addition of cobalt salt. Other process parameters were identical to those in Example 1. Product testing results showed that the magnesium oxide activity was 135 s and the specific surface area was 23.2 m². 2 The sample contains 98.1% magnesium oxide, has an average particle size of 2.1 µm, and an iodine adsorption value of 122 mg / g. The main process parameters of each embodiment and the differences between each comparative example and the embodiments are shown in Tables 1 and 2.

[0078] Table 1 Main process parameters of each embodiment

[0079] Sample number Raw material particle size (mm) Preheating temperature (°C) Temperature in the first temperature zone (°C) Temperature in the second temperature zone (°C) Heating rate (°C / min) Cooling rate (°C / min) Cobalt doping coefficient Example 1 5.0 250 700 900 18 35 5.5 Example 2 7.0 290 745 940 14 48 9.0 Example 3 3.5 210 660 860 6 22 1.5 Example 4 4.5 225 680 880 10 30 3.8

[0080] Table 2. Differences between Comparative Examples and Specific Examples

[0081] Comparative numbering Dual-temperature gradient calcination Pulse heating Magnetic field assistance cobalt salts Comparative Example 1 × × × × Comparative Example 2 √ √ × √ Comparative Example 3 √ × √ √ Comparative Example 4 √ √ √ ×

[0082] Notes: The process parameters in Table 1 are the main control parameters for each embodiment. In actual production, other parameters such as residence time, magnetic field strength, and pulse frequency are also included. In Table 2, "√" indicates that the technology is used, and "×" indicates that the technology is not used.

[0083] Comparative Experiments and Result Analysis: To verify the effects of each example and comparative example, a series of comparative experiments were designed to test the key performance indicators of the magnesium oxide products prepared in each example and comparative example. All test methods followed national or industry standards, and the activity test was conducted using the citric acid method. Specifically, 0.5g of magnesium oxide sample was weighed and added to 50mL of 0.07mol / L citric acid solution. The time it took for the solution temperature to rise from the initial temperature to the highest temperature was recorded under continuous stirring; this time was the activity value. The smaller the activity value, the faster the reaction rate of magnesium oxide with citric acid, and the higher the activity. The experiments were conducted in a constant temperature and humidity laboratory at 25℃ and 50% relative humidity. Each sample was tested three times, and the average value was taken as the final result. The test results showed that the activity of magnesium oxide prepared in Examples 1 to 4 was all above 140s, significantly better than that of Comparative Examples 1 to 4. Example 3 showed the highest activity, reaching 151s, which is related to its use of a lower temperature and a slower heating rate, which is beneficial for forming a fine and uniform crystal structure.

[0084] Specific surface area was measured using the BET nitrogen adsorption method. Before testing, the samples underwent vacuum degassing at 150°C for 4 hours to remove adsorbed moisture and gases from the surface. Then, the adsorption isotherm of nitrogen gas on the samples was measured at liquid nitrogen temperature, and the specific surface area was calculated using the BET equation. The test results showed that the magnesium oxide prepared in Examples 1 to 4 all had a specific surface area of ​​24 m². 2 The specific surface area was above / g, while that of comparative examples 1 to 4 was between 18.5 and 23.2 m². 2 The specific surface area is between / g. A larger specific surface area indicates that the product has more active sites, which is beneficial to improving its application performance in refractory materials, rubber, pharmaceuticals and other fields.

[0085] Magnesium oxide content was determined using EDTA titration. 0.2 g of magnesium oxide sample was weighed, dissolved in dilute hydrochloric acid, and the pH was adjusted to 10 with ammonia-ammonium chloride buffer solution. Titration was then performed using 0.05 mol / L EDTA standard solution, with Eriochrome Black T as the indicator. The magnesium oxide content was calculated based on the volume of EDTA consumed. pH and titration speed were strictly controlled throughout the experiment to ensure accurate endpoint determination. Test results showed that the magnesium oxide content prepared in all examples and comparative examples was above 97%, with Example 2 exhibiting the highest content at 98.5%, indicating more complete decomposition at higher temperatures.

[0086] Particle size distribution was tested using the laser diffraction method specified in GB / T19077-2016. A Mastersizer 3000 laser particle size analyzer (Malvern, UK) was used. A small amount of magnesium oxide sample was dispersed in anhydrous ethanol and sonicated for 5 minutes to ensure thorough dispersion before being injected into the test cell for measurement. The instrument automatically recorded the particle size distribution curve and calculated parameters such as average particle size, median particle size (D50, D10, and D90). The test results showed that the magnesium oxide prepared in Examples 1 to 4 had an average particle size between 1.5 and 2.2 µm, with a narrow particle size distribution and good uniformity. In contrast, Comparative Example 1 had an average particle size of 3.8 µm, a wider particle size distribution, and poorer uniformity. Fine and uniform particle size is beneficial for improving the dispersibility and reinforcing effect of magnesium oxide in composite materials.

[0087] The iodine adsorption value was tested according to the method specified in GB / T12496.8-2015. 0.1 g of magnesium oxide sample was weighed, and 25 mL of a 0.05 mol / L iodine solution was added. The solution was shaken in a constant temperature water bath at 25℃ for 30 min and then filtered. 10 mL of the filtrate was titrated with a 0.1 mol / L sodium thiosulfate standard solution, using starch as an indicator. The iodine adsorption amount was calculated based on the volume of sodium thiosulfate consumed. The iodine adsorption value reflects the porous structure and adsorption performance of magnesium oxide; a higher value indicates a stronger adsorption capacity. The test results showed that the iodine adsorption values ​​of Examples 1 to 4 were between 128 and 142 mg / g, significantly higher than the 95 to 122 mg / g of Comparative Examples 1 to 4, indicating that the magnesium oxide prepared by the method of this invention has a more developed pore structure and stronger adsorption capacity. The experimental results are shown in Table 3 and... Figures 1-7 As shown.

[0088] Table 3 Key performance indicators of each embodiment and comparative example

[0089] Sample number Activity level (seconds) <![CDATA[Specific surface area (m 2 / g)]]> MgO content (%) Average particle size (μm) Iodine adsorption value (mg / g) Example 1 148 26.8 98.2 1.8 135 Example 2 142 24.5 98.5 2.2 128 Example 3 151 28.2 97.8 1.5 142 Example 4 150 27.5 98.0 1.6 138 Comparative Example 1 108 18.5 97.2 3.8 95 Comparative Example 2 128 21.8 97.9 2.5 115 Comparative Example 3 132 22.5 98.0 2.3 118 Comparative Example 4 135 23.2 98.1 2.1 122

[0090] As can be seen from Table 3, the method for preparing highly active magnesium oxide by dual-temperature gradient calcination of magnesite described in this invention has significant technical advantages. Compared with Comparative Example 1, which uses a traditional single-temperature isothermal calcination method, the magnesium oxide prepared by the method of this invention exhibits increased activity by more than 37%, increased specific surface area by more than 44%, reduced average particle size by more than 52%, and increased iodine adsorption value by more than 42%.

[0091] Comparative Example 2, which did not use magnetic field-assisted technology, had performance indicators between those of Example 1 and Comparative Example 1, indicating that magnetic field assistance promotes magnesite decomposition and crystal orientation, increasing product activity by approximately 15%. Comparative Example 3, which did not use pulse heating technology, also showed a decrease in performance, indicating that pulse heating promotes decomposition by generating thermal stress, increasing product activity by approximately 12%.

[0092] Example 3, using a lower temperature and a slower heating rate, achieved the highest activity and specific surface area, but with relatively lower production efficiency. Example 2, using a higher temperature and a faster heating rate, achieved higher production efficiency, but with a slight decrease in activity and specific surface area. Examples 1 and 4, using moderate parameters, achieved a good balance between performance and efficiency. These results provide a basis for selecting appropriate process parameters based on actual needs in industrial production.

[0093] The results of the comparative experiment on magnesium oxide activity are as follows: Figure 1 As shown, activity is one of the core indicators for evaluating the quality of magnesium oxide products. This experiment uses the citric acid method specified in GB / T5984-1986 standard for determination. During the experiment, 0.5 g of magnesium oxide sample was added to 50 mL of a 0.07 mol / L citric acid solution. The time required for the solution temperature to rise from the initial temperature to the highest temperature was recorded under continuous stirring; this time is the activity value. A higher activity value indicates a faster reaction rate between magnesium oxide and citric acid, and higher chemical activity of the magnesium oxide. The test was conducted in a constant temperature and humidity laboratory, with the temperature controlled at 25℃ and the relative humidity at 50%. Each sample was tested three times, and the average value was taken to ensure the accuracy and reliability of the data.

[0094] from Figure 1 As shown in neutron plot a, the activity of magnesium oxide prepared in Examples 1 to 4 were 148 seconds, 142 seconds, 151 seconds, and 150 seconds, respectively, all significantly higher than the 108 seconds, 128 seconds, 132 seconds, and 135 seconds of Comparative Examples 1 to 4. In particular, the activity of Example 3 reached 151 seconds, which is a 39.8% improvement compared to the 108 seconds of Comparative Example 1, representing a very significant performance improvement. Figure 1 Neutron diagram b focuses on comparing Example 1 and Comparative Example 1, clearly showing that the activity of Example 1 is 148 seconds, which is 37.0% higher than that of Comparative Example 1 (108 seconds). The dual-temperature gradient calcination method of this invention, combining pulse heating and magnetic field assistance, significantly improves the activity of magnesium oxide. Dual-temperature gradient calcination achieves staged decomposition of magnesite. In the first temperature zone, the pulsed pre-decomposition, under the effect of periodic temperature fluctuations, generates alternating thermal stress within the magnesite particles, promoting the formation of microcracks in the crystal structure and creating channels for the escape of carbon dioxide gas, thus preventing the formation of a surface sintered layer from hindering internal decomposition. Simultaneously, the applied alternating magnetic field affects ion migration and crystal orientation. Under the gradually increasing magnetic field, magnesite undergoes three stages: pre-decomposition, crystal orientation, and lattice rearrangement, promoting the directional growth of magnesium oxide crystals and forming a crystal structure with more active sites. The complete decomposition stage in the second temperature zone ensures the complete decomposition of the remaining magnesium carbonate in the magnesite. Real-time monitoring of the outlet carbon dioxide concentration and dynamic adjustment of the residence time guarantee the high purity and high activity of the product.

[0095] Figure 1 As can be seen, the highest activity level in Example 3 was 151 seconds, while the activity level in Example 2 was relatively low at 142 seconds. Example 3 employed a lower calcination temperature and a slower heating rate, with the first temperature zone at 660°C and the second temperature zone at 860°C. This temperature regime is conducive to the formation of fine and uniform magnesium oxide crystals. Small grain size means a large specific surface area and more active sites, thus resulting in high activity. In contrast, Example 2 used higher temperatures, with the first temperature zone at 745°C and the second temperature zone at 940°C. The high temperature promoted grain growth, and although the decomposition was more complete, the increased grain size led to a decrease in specific surface area, resulting in a slight decrease in activity. This indicates that within the parameter range defined in this invention, appropriately lowering the temperature is beneficial for obtaining a highly active product, but excessively low temperatures can lead to incomplete decomposition. Therefore, it is necessary to find an optimal balance between complete decomposition and grain size.

[0096] Comparative Example 1, using a traditional single-zone isothermal calcination method, had an activity level of only 108 seconds, the lowest among all samples. Comparative Example 2, without magnetic field assistance, had an activity level of 128 seconds, 13.5% lower than Example 1's 148 seconds, indicating that magnetic field assistance improved activity by approximately 15%. Comparative Example 3, without pulse heating, had an activity level of 132 seconds, 10.8% lower than Example 1, indicating that pulse heating improved activity by approximately 12%.

[0097] Specific surface area is an important indicator reflecting the microstructure of magnesium oxide and directly affects its performance in practical applications. Figure 2 The specific surface area of ​​magnesium oxide was determined using the BET nitrogen adsorption method in a comparative experiment. Before the experiment, the samples were degassed under vacuum at 150℃ for 4 hours to remove adsorbed moisture and gas, ensuring consistency of the testing standards. Then, the adsorption isotherm of nitrogen on the samples was measured at liquid nitrogen temperature (-196℃), and the specific surface area was calculated using the BET equation. A larger specific surface area indicates a larger surface area per unit mass of magnesium oxide, implying more active sites and stronger adsorption and catalytic capabilities.

[0098] from Figure 2 Neutron plot a shows that the specific surface areas of Examples 1 to 4 are 26.8, 24.5, 28.2, and 27.5 m², respectively. 2 / g, while the specific surface areas of Comparative Examples 1 to 4 were 18.5, 21.8, 22.5, and 23.2 m², respectively. 2 / g. Figure 2 The most striking comparison is between Example 3 and Comparative Example 1, as illustrated in subfigure b, where Example 3 exhibits a specific surface area of ​​28.2 m². 2 / g, compared to 18.5m in Comparative Example 1 2The specific surface area increased by 52.4%, which is a very considerable improvement. Example 1 had a specific surface area of ​​26.8 m². 2 The specific surface area (SSA) was increased by 44.9% compared to Comparative Example 1, demonstrating a significant advantage. During the dual-temperature gradient calcination process, the pulsed heating in the first temperature zone caused the magnesite to repeatedly undergo heating and relative cooling during temperature fluctuations. This thermal cycle promoted the formation of numerous microcracks and defects within the crystal, increasing the internal surface area. The alternating magnetic field further promoted the propagation of these microcracks and the formation of new surfaces. Under the influence of the magnetic field, the newly formed magnesia crystals underwent directional alignment, resulting in a more porous and loose crystal structure rather than a dense, blocky structure. Although the temperature in the second temperature zone was higher, the precise control of the residence time prevented a decrease in specific surface area due to over-sintering. The rapid cooling process fixed the porous crystal structure, preventing further grain growth and pore closure during slow cooling. Example 3, using the lowest temperature parameters, achieved the largest specific surface area of ​​28.2 m². 2 / g. Example 2 used the highest temperature parameters, with a specific surface area of ​​24.5m². 2 The specific surface area (SSA) was significantly higher than in all comparative examples, but relatively lower in this example. At higher temperatures, the thermal motion of atoms intensifies, the grain boundary migration rate accelerates, the driving force for small grains to merge into large grains increases, and grain growth leads to a decrease in the total grain boundary area, thus reducing the specific surface area. At lower temperatures, although atoms still have some migration capacity to complete the decomposition reaction, the grain growth rate is slower, maintaining a small grain size and a large specific surface area. Magnetic field-assisted technology significantly contributes to the specific surface area; Comparative Example 2, which does not use a magnetic field, has a specific surface area 18.7% lower than that of Example 1. The magnetic field affects the crystal growth pattern, promoting the formation of a loose and porous structure.

[0099] Figure 3 A normalization method was employed to unify the three dimensional indicators—activity, specific surface area, and iodine adsorption value—within a dimensionless range of 0 to 100, allowing for intuitive comparison within the same coordinate system. The normalization method involved dividing each indicator by its maximum value across all samples and then multiplying by 100. This resulted in a normalized value of 100 for the optimal sample, with the normalized values ​​for other samples proportionally reduced. Figure 3 Different line types and markings are used to distinguish different indicators and sample groups. The examples are represented by solid lines, the comparative examples by dashed lines, the activity is marked by circles, the specific surface area is marked by squares, and the iodine adsorption value is marked by triangles. Through the combination of color, line type and markings, the meaning of each curve can be clearly identified.

[0100] from Figure 3A significant difference in overall performance can be observed between the Example Group and the Comparative Example Group. The three indicator lines for Examples 1 to 4 are all at relatively high levels, with normalized values ​​mostly above 90, forming a high-performance region. In contrast, the three indicator lines for Comparative Examples 1 to 4 are all at relatively low levels, with normalized values ​​mostly below 80, forming a low-performance region. Figure 3 Example 3 showed normalized values ​​of 100 or close to 100 for both activity and specific surface area, indicating optimal overall performance. Example 2 had a relatively low normalized value of approximately 94 for activity, but performed well in other indicators, consistent with its use of a higher temperature parameter, which resulted in a slight decrease in activity but more complete decomposition. However, from... Figure 3 As can be seen, the embodiment outperforms the comparative example in terms of activity, specific surface area, and iodine adsorption value, without any instance of one indicator improving while another decreases, achieving synergistic optimization of multiple indicators. Dual-temperature gradient calcination, through staged temperature control, ensures the integrity of decomposition while avoiding over-sintering. Pulse heating promotes decomposition while increasing the internal surface area. Magnetic field assistance not only promotes decomposition but also influences crystal orientation, forming a porous structure, increasing both activity and specific surface area. A large specific surface area, in turn, leads to strong adsorption capacity, i.e., a high iodine adsorption value. High activity means a faster reaction between magnesium oxide and citric acid, due to more active sites participating in the reaction. Active sites are mainly distributed on the crystal surface, grain boundaries, and defects; a large specific surface area means more surface atoms, thus more active sites. Iodine adsorption value reflects magnesium oxide's adsorption capacity for iodine molecules. Adsorption mainly occurs on the surface and in pores; magnesium oxide with a large specific surface area and well-developed pores has a strong adsorption capacity. Therefore, activity, specific surface area, and iodine adsorption value reflect the characteristics of magnesium oxide's microstructure from different perspectives, and their consistent trends are reasonable. Furthermore, the three index lines of Comparative Examples 2, 3, and 4 are quite similar, with little difference in normalized values, while they differ significantly from those of the Example Group.

[0101] Particle size distribution is an important physical property of magnesium oxide products, which directly affects its dispersibility in composite materials, its stability in suspensions, and its reaction rate in chemical reactions. Figure 4The average particle size of magnesium oxide was determined using laser diffraction. Before testing, a small amount of magnesium oxide sample was dispersed in anhydrous ethanol and then sonicated for 5 minutes. The cavitation effect of the ultrasound broke up the particle agglomerates, allowing the particles to be fully dispersed into primary particles. The dispersed suspension was then injected into the instrument's test cell. When the laser beam passed through the suspension, it was scattered. Particles of different sizes produced scattered light at different angles and intensities. The instrument measured the spatial distribution of the scattered light and used Mie scattering theory to deduce the particle size distribution. The instrument provided several statistical parameters, including the average particle size, median particle size D50, and D10 and D90.

[0102] from Figure 4 As can be seen from neutron graph a, the average particle sizes of Examples 1 to 4 are 1.8, 2.2, 1.5 and 1.6 micrometers, respectively, while the average particle sizes of Comparative Examples 1 to 4 are 3.8, 2.5, 2.3 and 2.1 micrometers, respectively. Figure 4 The most significant comparison is between Example 3 and Comparative Example 1. The average particle size of Example 3 is only 1.5 micrometers, while the average particle size of Comparative Example 1 reaches 3.8 micrometers. The particle size of Example 3 is 60.5% smaller than that of Comparative Example 1. Figure 4Neutron diagram b calculated and compared the average particle size of the example group and the comparative group. The average particle size of the example group was 1.78 μm, while that of the comparative group was 2.68 μm, representing a 33.6% reduction in particle size. This significant reduction in particle size has a crucial impact on the performance of magnesia in practical applications. When used in refractory materials, finer magnesia particles are more uniformly distributed in the matrix, improving the material's density and strength. During the pulsed pre-decomposition process in the first temperature zone, the periodic temperature fluctuations caused the magnesite particles to repeatedly expand and contract, and the mechanical stress promoted the breakage of large particles into smaller ones. The alternating magnetic field further promoted particle refinement, and the electromagnetic force induced by the magnetic field acted on charged ions and defects, hindering excessive grain growth to some extent. In the complete decomposition stage of the second temperature zone, precise control of temperature and residence time ensured complete decomposition while avoiding grain coarsening caused by prolonged high temperatures. The rapid cooling process promptly terminated the grain growth process, fixing the fine particle size. Example 2 used the highest temperature parameters, resulting in an average particle size of 2.2 μm, the largest among the examples. Example 3 used the lowest temperature parameters, resulting in an average particle size of 1.5 micrometers, the smallest among the examples. The physical reason for this pattern is that as temperature increases, the thermal kinetic energy of atoms increases, the diffusion coefficient increases, the grain boundary migration rate accelerates, and the process of small grains merging into large grains is accelerated. This is a thermodynamically spontaneous process because the total interfacial energy of large grains is lower than that of small grains, and the system tends to reduce the total energy. At lower temperatures, although the decomposition reaction can still occur, the grain growth rate is slower, maintaining a fine particle size. This pattern is consistent with the change in specific surface area with temperature, because small particle size means large specific surface area; they reflect the microstructural characteristics of magnesium oxide from different perspectives. Comparative Example 1 used conventional single-temperature zone isothermal calcination, calcining at a constant temperature of 850°C for a long time for 60 minutes. Under these process conditions, the grains had sufficient time to grow, thus forming coarse particles.

[0103] Iodine adsorption value is an important indicator for evaluating the adsorption performance of magnesium oxide, reflecting the degree of development of the pore structure and surface chemical properties of magnesium oxide. Figure 5 The iodine adsorption value was determined by the iodine adsorption method in the comparative experiment. Figure 5The experimental procedure involves weighing 0.1 g of magnesium oxide sample and adding 25 mL of a 0.05 mol / L iodine solution (the iodine solution is brownish-red). The mixture is then placed in a 25°C constant-temperature water bath and shaken for 30 minutes. Shaking promotes sufficient contact between the magnesium oxide and the iodine solution, allowing adsorption to reach equilibrium. Immediately after 30 minutes, the mixture is filtered. 10 mL of the filtrate is titrated with a 0.1 mol / L sodium thiosulfate standard solution, using starch as an indicator. During titration, iodine reacts with sodium thiosulfate in a redox reaction; the endpoint is reached when the solution changes from blue to colorless. The amount of iodine remaining in the filtrate can be calculated based on the volume of sodium thiosulfate consumed. Subtracting the remaining iodine from the initial amount added gives the amount of iodine adsorbed by the magnesium oxide. Dividing this by the mass of magnesium oxide yields the iodine adsorption value, expressed in mg / g. A higher iodine adsorption value indicates a stronger ability of magnesium oxide to adsorb iodine, indirectly reflecting a more developed pore structure, larger specific surface area, and more surface active sites.

[0104] from Figure 5 It can be observed that the iodine adsorption values ​​of Examples 1 to 4 are 135, 128, 142 and 138 mg / g, respectively, and the iodine adsorption values ​​of Comparative Examples 1 to 4 are 95, 115, 118 and 122 mg / g, respectively. Figure 5 Different marker shapes were used to distinguish between the examples and comparative examples. Examples were marked with circles, while comparative examples were marked with squares. A trend line was plotted for each group of data. The scatter points for the example group were all located in the upper high-value region of the graph, and the trend line showed a slight upward trend, indicating that the iodine adsorption values ​​among the examples were relatively similar and maintained at a high level. The scatter points for the comparative example group were all located in the lower low-value region of the graph, and the trend line also showed an upward trend but with a steeper slope, indicating significant differences between the comparative examples. The iodine adsorption values ​​gradually increased from Comparative Example 1 to Comparative Example 4. The highest iodine adsorption value was found in Example 3, at 142 mg / g, which was 49.5% higher than the 95 mg / g of Comparative Example 1. Iodine adsorption mainly occurred on the surface and in the pores of magnesium oxide, with iodine molecules binding to the magnesium oxide surface through physical or chemical adsorption. The high iodine adsorption value indicates that magnesium oxide not only has a large specific surface area but also a well-developed pore structure and large pore volume. The formation mechanism of the well-developed porous structure involves the decomposition of magnesite during dual-temperature gradient calcination, releasing a large amount of carbon dioxide gas. As this gas escapes from the interior of the particles, it leaves numerous pore channels within the magnesium oxide. The thermal stress generated by pulse heating induces microcracks in the particles, which also contribute to the porous structure. An alternating magnetic field promotes gas escape and pore formation; the micro-eddies and thermal effects induced by the magnetic field help open up gas diffusion channels. Rapid cooling fixes the porous structure, preventing pore closure during slow cooling. This well-developed porous structure not only enhances the iodine adsorption value but also, in practical applications, means that magnesium oxide possesses stronger functions in adsorbing harmful substances, catalyzing chemical reactions, and serving as a carrier for loading active components. Figure 5Example 3 exhibits the highest iodine adsorption value of 142 mg / g, the highest activity of 151 seconds, and the largest specific surface area of ​​28.2 m². 2 / g. The iodine adsorption value of 128 mg / g in Example 2 is the lowest among the examples, with an activity of 142 seconds and a specific surface area of ​​24.5 m². 2 / g is also relatively low in the examples.

[0105] Figure 6 The four sub-graphs systematically analyze the influence of calcination temperature parameters on the properties of magnesium oxide, providing a theoretical basis for optimizing process parameters. Figure 6 Only data from Examples 1 to 4 were used in this study. Figure 6 Neutron plots a and c investigate the effect of temperature in the first temperature zone, subplots b and d investigate the effect of temperature in the second temperature zone, subplots a and b investigate the effect on activity, and subplots c and d investigate the effect on contrast surface area. Each subplot includes scatter plots and fitted trend lines, which are linearly fitted.

[0106] from Figure 6 Neutron plot a shows that the lowest temperature in the first temperature zone of Example 3 was 660℃, and the highest activity was 151 seconds. In Example 2, the highest temperature in the first temperature zone was 745℃, and the activity was relatively low at 142 seconds. The negative slope of the trend line indicates that an increase in the temperature of the first temperature zone leads to a decrease in activity. The reason for this pattern is that the first temperature zone mainly completes the pre-decomposition process. At this stage, the temperature should not be too high; a moderate temperature is conducive to the formation of uniform and fine pre-decomposition products, laying a good foundation for the complete decomposition in the second temperature zone. If the temperature is too high, the decomposition rate in the first temperature zone is too fast, which may lead to rapid surface decomposition forming a dense layer that hinders internal decomposition, or cause local overheating leading to uneven decomposition. A appropriately lower first temperature zone makes the decomposition process more gentle and controllable, which is conducive to the formation of highly active products. Figure 6 Neutron plot b shows that the temperature in the second temperature zone also exhibits a negative correlation with the activity, but the correlation is not as pronounced as in the first temperature zone. In Example 2, the highest second temperature zone temperature was 940°C, with an activity of 142 seconds. In Example 3, the lowest second temperature zone temperature was 860°C, with an activity of 151 seconds. The second temperature zone primarily completes the final decomposition; the temperature needs to be high enough to ensure complete decomposition. However, excessively high temperatures can lead to grain coarsening and a decrease in specific surface area, thereby reducing activity. The selection of the second temperature zone temperature needs to find a balance between decomposition completeness and grain size. Within the range of 850 to 950°C defined in this invention, complete decomposition can be guaranteed; therefore, a relatively lower temperature can be chosen to obtain higher activity. From... Figure 6 Neutron plot c shows a clear negative correlation between temperature and specific surface area in the first temperature zone. In Example 3, the first temperature zone temperature was 660℃, and the specific surface area was 28.2 m². 2 / g. Example 2: First temperature zone temperature 745℃, specific surface area 24.5m². 2 / g. The steep slope of the trend line indicates that the temperature in the first temperature zone has a significant impact on the specific surface area. The size and number of initial magnesium oxide nuclei formed during the pre-decomposition stage in the first temperature zone have a decisive influence on the specific surface area of ​​the final product. Lower temperatures favor the formation of a large number of fine nuclei, which grow in subsequent processes but still maintain a relatively small size. Higher temperatures result in fewer but larger nuclei, leading to a smaller final specific surface area. From Figure 6 Neutron plot d shows a negative correlation between temperature and specific surface area in the second temperature region. In Example 2, the second temperature region has a temperature of 940℃ and a specific surface area of ​​24.5 m². 2 / g. The second temperature zone of Example 3 was 860℃, with a specific surface area of ​​28.2 m². 2 / g. While the high temperature in the second temperature zone ensures complete decomposition, it also promotes grain growth and reduces the specific surface area. The effect of temperature is more pronounced when the residence time in the second temperature zone is long. Therefore, while ensuring complete decomposition, a relatively low second temperature and a short residence time should be chosen. From Figure 6 It can be concluded that appropriately lowering the calcination temperature is beneficial to improving the activity and specific surface area of ​​magnesium oxide. However, the temperature should not be lowered too much, otherwise incomplete decomposition will occur. This invention limits the temperature of the first temperature zone to 650 to 750°C and the temperature of the second temperature zone to 850 to 950°C. Within this range, the optimal product performance is obtained near the lower limit of the temperature, and the higher production efficiency is obtained near the upper limit of the temperature. Appropriate temperature parameters can be selected according to different focuses on product performance and production efficiency.

[0107] Figure 7 A heatmap is used to visually display the performance indicators of each sample across multiple aspects. The heatmap uses color intensity to represent numerical values. Figure 7 The horizontal axis represents five performance indicators: activity, specific surface area, magnesium oxide content, particle size optimization, and iodine adsorption value. The particle size optimization indicator underwent reverse normalization, as smaller particle size is generally better. For the other indicators, larger values ​​are generally better. To ensure consistent optimization across all indicators, the particle size indicator was converted to 100 minus the normalized particle size value; for all indicators, larger values ​​are generally better. The vertical axis represents eight samples, from top to bottom: Examples 1 to 4 and Comparative Examples 1 to 4. The color of each cell in the graph corresponds to the normalized score of that sample for that indicator.

[0108] from Figure 7 As can be seen, the four rows corresponding to Examples 1 to 4 are predominantly warm-toned, with most cells being orange or red, indicating high performance. In contrast, the four rows corresponding to Comparative Examples 1 to 4 are predominantly cool-toned. Figure 7The row containing Example 3 is almost entirely dark red, especially in terms of activity, specific surface area, and iodine adsorption value, where it reaches or approaches the highest score of 1.0, indicating that Example 3 has the best overall performance. The row containing Comparative Example 1 is mostly dark blue, especially in terms of activity, specific surface area, particle size optimization, and iodine adsorption value, where it scores very low, inferior to other samples. Figure 7 In the examples, no blue squares appeared in any row, indicating that all indicators reached a high level. Dual-temperature gradient calcination ensured both high activity and large specific surface area, as well as high purity and fine particle size. Pulse heating promoted crystal refinement and pore formation, improving multiple properties. Magnetic field-assisted optimization of crystal structure and orientation enhanced activity and adsorption capacity. Example 3 performed best in four indicators: activity, specific surface area, particle size optimization, and iodine adsorption value, all showing deep red. Example 2 performed best in magnesium oxide content, as its higher temperature resulted in more complete decomposition. Examples 1 and 4 showed relatively balanced overall performance, with all indicators at a high level. If the application requires extremely high activity and specific surface area, the process parameters of Example 3 can be selected. If the application requires higher purity but relatively less stringent activity requirements, the process parameters of Example 2 can be selected. If a product with good overall performance and high process stability is required, the process parameters of Example 1 or Example 4 can be selected.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing highly active magnesium oxide by dual-temperature-zone gradient calcination of magnesite, characterized in that, Includes the following steps: S1: Raw material pretreatment; crush the magnesite raw material to a particle size of 3-8mm and preheat it to 200-300℃ in a preheating device; S2: First temperature zone pulsed pre-decomposition; the preheated magnesite is sent into the first temperature zone and pulsed heating is carried out in the temperature range of 650-750℃, with a temperature fluctuation range of ±20-40℃. At the same time, an alternating magnetic field is applied, and the residence time is 15-25min. The CO2 concentration is monitored in real time and the temperature and residence time are adjusted according to the CO2 concentration feedback. S3: Heating in the transition zone; heating the material to 850-880℃ at a heating rate of 5-15℃ / min; S4: Complete decomposition in the second temperature zone; The material is sent into the second temperature zone and treated at a constant temperature of 850-950℃ for 25-40 minutes. The CO2 concentration at the outlet is monitored and the residence time is dynamically adjusted according to the CO2 concentration to reduce the CO2 concentration at the outlet to below 3%. S5: Cooling and collection; rapidly cool the calcined magnesium oxide to below 200℃ at a cooling rate of 20-50℃ / min, and obtain highly active magnesium oxide after sieving.

2. The method according to claim 1, characterized in that, In step S1, a cobalt salt solution is sprayed onto the surface of the magnesite before preheating. The specific operation is as follows: Cobalt nitrate or cobalt acetate solution is sprayed onto the surface of the crushed magnesite through an atomizing nozzle. The amount of cobalt salt added... Calculate using the following formula: ;in, This refers to the mass of cobalt in the cobalt salt; α represents the mass of magnesite raw material; α is the cobalt doping coefficient, with a value of 1-10. During spraying, the material is stirred or turned over simultaneously to ensure that the cobalt salt solution is evenly distributed. After spraying, the material is immediately sent to a preheating device. During the preheating process at 200-300℃, the cobalt salt solution evaporates, and cobalt ions adhere to the surface of the magnesite particles, forming a cobalt-doped precursor. This ensures that the cobalt salt is evenly dispersed and adheres to the particle surface during the preheating process of the sprayed magnesite.

3. The method according to claim 1, characterized in that, In step S2, the specific operations of the first temperature zone pulse pre-decomposition, CO2 concentration feedback adjustment, and magnetic field gradient control are as follows: Pulse temperature control: Set the reference temperature for the first temperature zone. The target temperature is set within the range of 650-750℃, and the actual temperature is achieved by periodically adjusting the heating power. exist Fluctuations within a range, of which The temperature range is 20-40℃, with a temperature fluctuation period. Determine by the following formula: in, This refers to the temperature fluctuation period; The pulse frequency; CO2 concentration feedback control: Set up 3-5 CO2 concentration monitoring points along the material flow direction in the first temperature zone, collect the CO2 concentration values ​​of each monitoring point in real time, and calculate the weighted average concentration. ,according to With target concentration Deviation adjustment dwell time, adjusted dwell time Calculate using the following formula: ; in, The adjusted dwell time; The baseline stay time; This is an adjustment coefficient, with a value ranging from 0.15 to 0.

25. This represents the weighted average CO2 concentration. The target CO2 concentration is set at 5%–7%; when At this time, the residence time can be extended by reducing the material conveying rate or increasing the baffle opening; when At the same time, the dwell time can be shortened by increasing the material conveying rate or reducing the baffle opening. Magnetic field gradient control: The first temperature zone is divided into three sections along its length: an inlet section, a middle section, and an outlet section, with a length ratio of 1:1.5:

1. A magnetic field strength of [insert value here] is applied to the inlet section. The magnetic field frequency is 0.02-0.03T. The frequency is 10-20 Hz; a magnetic field strength is applied in the middle section. The magnetic field frequency is 0.04-0.06T. The frequency is 25-35 Hz; the magnetic field strength applied at the exit section is... The magnetic field frequency is 0.06-0.08T. The frequency is 40-50Hz; each magnetic field segment is controlled by an independent frequency converter power supply, and the magnetic field strength and frequency between adjacent segments transition smoothly, with a transition zone length of 0.3-0.5m; The alternating magnetic field is activated at the same time the material enters the first temperature zone, so that the material undergoes pre-decomposition under the combined action of pulsed temperature and gradient magnetic field. Under the action of gradually increasing magnetic field, it goes through three stages: pre-decomposition, crystal orientation and lattice rearrangement, which promotes CO2 escape and directional growth of MgO crystals.

4. The method according to claim 1, characterized in that, In step S3, the specific operation of heating the transition zone is as follows: Control the temperature of the material exiting the first temperature zone Linear heating to the inlet temperature of the second temperature zone heating rate Calculate using the following formula: ;in, The heating rate; The inlet temperature for the second temperature zone is 850-880℃. The outlet temperature of the first temperature zone is 730-760℃. This is the transition time, with a value of 5-10 minutes. During the heating process, the atmosphere is kept flowing, and the flow rate increases with the temperature to promote the discharge of residual CO2 and prevent the product from being recarbonized.

5. The method according to claim 1, characterized in that, In step S4, the specific operation for the complete decomposition of the second temperature zone is as follows: The set value for maintaining the temperature of the second temperature zone constant within the range of 850-950℃. The heating power is adjusted in real time through a PID control algorithm. The control algorithm is as follows: ; in, This refers to the adjusted heating power. The reference heating power; This is the proportionality coefficient; The integral coefficient; These are the differential coefficients; For temperature deviation, ; For the actual measured temperature; This is the integral of the temperature deviation over time. This is the derivative of the temperature deviation with respect to time. CO2 concentration was monitored at the outlet of the second temperature zone. ,according to Dynamically adjust material residence time The formula is adjusted as follows: ； in, This is the adjusted stay time; The baseline stay time; The adjustment factor is set to a value between 0.2 and 0.

3. The CO2 concentration at the export point; For reference concentration, the value is 3%.

6. The method according to claim 1, characterized in that, In step S5, the specific operation of cooling and collecting is as follows: Set the outlet temperature of the second temperature zone to The magnesium oxide is fed into a cooling device and cooled to the outlet temperature by indirect water cooling or forced air cooling. Cooling rate Controlled by the following formula: ; in, Cooling rate; This refers to the inlet temperature of the cooler. The outlet temperature of the cooler should be controlled between 180-220℃. Cooling time; The cooling rate is maintained within the range of 20-50℃ / min by adjusting the flow rate of the cooling medium; a protective gas is introduced during the cooling process to prevent magnesium oxide from absorbing moisture; the cooled magnesium oxide is then classified by a vibrating screen to separate different grades of products with particle sizes of <1mm, 1-3mm, and 3-5mm.

7. A system for preparing highly active magnesium oxide by dual-temperature gradient calcination of magnesite according to any one of claims 1-6, characterized in that, include: The raw material pretreatment unit includes a crusher, a screening machine, a cobalt salt spraying device, and a cyclone preheater connected in sequence; A swirl-type dual-temperature zone calcination reactor includes a reactor cylinder, a spiral guide plate, and an adjustable baffle. The reactor cylinder is provided with a first temperature zone, a transition zone, and a second temperature zone along its length. The spiral guide plate is installed on the inner wall of the reactor cylinder to make the material flow in a spiral. The adjustable baffle is installed between the first temperature zone and the transition zone, and between the transition zone and the second temperature zone, to adjust the material flow rate and residence time. The pulse heating and magnetic field-assisted system includes a pulse heating controller, an array of electric heating elements, a magnetic field generator, and a cooling system. The pulse heating controller is electrically connected to the array of electric heating elements to control the periodic fluctuation of the temperature in the first temperature zone. The magnetic field generator includes multiple sets of electromagnetic coils distributed along the circumference of the first temperature zone. Each set of electromagnetic coils is independently powered by a frequency converter to generate an alternating magnetic field with a gradient distribution along the axial direction. The cooling system is connected to the electromagnetic coils to maintain the operating temperature of the electromagnetic coils. The temperature control and atmosphere conditioning system includes a temperature acquisition module, a CO2 concentration monitoring module, an atmosphere conditioning module, and a central controller. Multiple temperature sensors of the temperature acquisition module are distributed in each temperature zone of the reactor. Multiple CO2 sensors of the CO2 concentration monitoring module are distributed at the inlet and outlet positions of the first and second temperature zones. The atmosphere conditioning module includes a flow meter, a regulating valve, and a fan. The central controller receives signals from the temperature acquisition module and the CO2 concentration monitoring module and outputs control commands to the pulse heating controller, the magnetic field generator, and the atmosphere conditioning module. The rapid cooling and product collection unit includes a cooler, a screening machine, and a product storage tank connected in series. The cooler inlet is connected to the outlet of the second temperature zone of the reactor, the cooler outlet is connected to the inlet of the screening machine, and the screening machine outlet is connected to the product storage tank.

8. The system according to claim 7, characterized in that: The swirling dual-temperature zone calcination reactor is equipped with: The spiral guide plate is made of metal sheet and is welded or fixed to the inner wall of the reactor cylinder in a spiral shape. The pitch of the spiral guide plate is 0.8-1.2m and the lead angle is 15-25°. 3-5 complete spirals are arranged along the axial direction. The adjustable baffle is made of heat-resistant alloy plate and is driven by a hydraulic or electric push rod. One end of the push rod is fixed to the outer wall of the reactor, and the other end is connected to the baffle. The baffle can extend and retract in the radial direction of the reactor to adjust the cross-sectional area of ​​the channel. The extension and retraction stroke of the push rod is controlled by the central controller according to the material flow rate and CO2 concentration signal. The pulse heating and magnetic field-assisted system is equipped with: The heating element array includes multiple heating elements distributed along the circumference and axial direction of the first temperature zone. The axial direction is divided into an inlet layer, an intermediate layer, and an outlet layer. The heating elements in each layer are independently grouped, and the power of each group is independently controlled by a pulse heating controller. The magnetic field generating device has multiple sets of electromagnetic coils divided into three sections along the axial direction of the first temperature zone. Each section contains 2-4 sets of electromagnetic coils. Each section of electromagnetic coils is connected to an independent frequency converter. The frequency converter is controlled by a central controller and outputs alternating currents of different intensities and frequencies, so that each section generates magnetic fields of different intensities and frequencies. The cooling system includes cooling water pipes and a circulating pump. The inlet and outlet of the cooling water pipes are respectively connected to the cooling jacket of the electromagnetic coil shell. The circulating pump drives the cooling water to circulate in the pipes.

9. The system according to claim 7, characterized in that: The temperature acquisition module of the temperature control and atmosphere conditioning system includes 16-24 thermocouple temperature sensors, with 6-8 sensors in the first temperature zone, 2-4 in the transition zone, and 8-12 in the second temperature zone. The signal terminals of each sensor are connected to the data acquisition card of the central controller via compensating wires. The CO2 concentration monitoring module includes 8-12 infrared CO2 sensors, with 2-3 sensors each at the inlet, middle, and outlet of the first temperature zone, and 2-3 at the outlet of the second temperature zone. Each sensor is mounted on a sampling probe that extends into the reactor. A sampling pump draws the flue gas to... The sensor measurement chamber connects the sensor output signals to the central controller. In the atmosphere control module, the flow meter is installed on the gas inlet pipe, the regulating valve is installed downstream of the flow meter, and the fan is installed at the tail of the reactor. The signal output of the flow meter and the control input of the regulating valve are both connected to the central controller. The fan is connected to the central controller via a frequency converter. The central controller uses an industrial computer and PLC architecture. The industrial computer runs the control software, and the PLC performs real-time control. The industrial computer and PLC are connected via a communication interface. The PLC's inputs are connected to the signals from each sensor, and its outputs are connected to each actuator. In the raw material pretreatment unit, the cobalt salt spraying device includes a solution storage tank, a metering pump, atomizing nozzles, and a spraying controller. The solution storage tank is connected to the inlet of the metering pump through a pipeline, and the outlet of the metering pump is connected to the atomizing nozzles through a pipeline. The atomizing nozzles are arranged on the conveying channel between the screening machine and the preheater, with 3-6 atomizing nozzles arranged along the circumference of the conveying channel. The spraying controller is communicatively connected to the central controller, receives material flow signals, calculates the amount of cobalt salt added, outputs control commands to the metering pump, and adjusts the flow rate of the metering pump.

10. The system according to claim 7, characterized in that, In the rapid cooling and product collection unit: The cooler is a vertical cooling tower with multiple layers of cooling plates inside. Material descending channels are formed between the cooling plates. The cooling plates are connected to cooling water pipes or air coolers. A discharge device is installed at the bottom of the cooler and is connected to the feed inlet of the screening machine. The screening machine is a multi-layer vibrating screen, including a first screen, a second screen, and a third screen arranged in sequence. The first screen has an aperture of 1mm, the second screen has an aperture of 3mm, and the third screen has an aperture of 5mm. Each screen has a corresponding discharge port below it. The product storage tank is a sealed tank with a feed inlet and a protective gas interface at the top and a discharge valve at the bottom. The feed inlet is connected to the discharge ports of the screening machine through pipes.

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